Measuring flow in an underground pipeline is not as simple as installing a conventional flow meter in a clean industrial pipe.
Underground drainage and wastewater pipelines often have large pipe diameters, changing water levels, sediment, suspended solids, debris, air bubbles, and alternating full-pipe and partially filled conditions. These factors can make conventional flow measurement difficult, especially when the equipment is installed inside the pipeline, and regular maintenance is inconvenient.
This is where an underground pipeline flow meter designed specifically for complex pipeline conditions can provide a more practical solution.
A radar ultrasonic flow meter combines radar flow measurement and ultrasonic measurement in one system. It can automatically switch between measurement modes according to pipeline conditions while monitoring flow velocity, water level, and flow rate.
For underground drainage networks where installation space is limited and maintenance access is difficult, this integrated approach provides a flexible solution for continuous flow monitoring.
What Is an Underground Pipeline Flow Meter?
An underground pipeline flow meter is a specialized flow measurement system designed to monitor water flow inside large underground pipelines, drainage networks, wastewater pipes, and other difficult-to-access water channels.
Unlike a conventional inline flow meter, which is installed directly into the pipeline and normally requires the liquid to pass through the meter body, an underground pipeline flow meter can be installed at the top of the pipeline.
This design is particularly useful for existing drainage and wastewater networks where cutting the pipe, modifying the pipeline, or installing measurement components directly inside the water flow can increase installation and maintenance difficulties.
The radar ultrasonic flow meter discussed in this article takes this concept further by integrating radar flow velocity measurement, ultrasonic flow velocity measurement, and water-level measurement into one compact system.
Instead of relying on a single measurement principle, it combines complementary technologies to adapt to changing pipeline conditions, including both partially filled and full-pipe operation.
The result is an integrated system designed to continuously monitor the hydraulic condition of an underground pipeline without requiring multiple separate instruments.
What Components Make Up an Underground Pipeline Flow Meter?
An integrated radar ultrasonic flow meter typically combines several measurement, processing, communication, and protection components:
- Radar flow velocity sensor – Measures surface flow velocity in suitable partially filled pipeline conditions without being immersed in wastewater.
- Ultrasonic flow velocity sensor – Provides an additional flow velocity measurement method when the pipeline operates under full-pipe conditions.
- Water-level sensor – Determines the height of the water inside the pipeline.
- Flow calculation unit – Processes flow velocity, water-level information, and pipeline geometry to calculate flow rate.
- Data acquisition and communication module – Collects, stores, and transmits measurement data.
- Protective housing – Protects the electronics and sensing components from water, dust, and harsh underground conditions.
- Mounting bracket – Secures the system at the selected measurement position.
These components work together as one integrated measurement system rather than functioning as separate instruments.
The system collects hydraulic data and processes it through an integrated flow calculation algorithm to determine the flow rate.
The working principle of the radar ultrasonic flow meter is based on complementary radar and ultrasonic measurement technologies.
How Does an Underground Pipeline Flow Meter Work?
Instead of forcing a single measurement method to operate under every possible pipeline condition, the system uses different measurement methods for different operating states.
Radar Flow Measurement
When the pipeline is partially filled, the radar sensor can measure the movement of water from above without direct contact with the wastewater.
This non-contact measurement approach is particularly useful in underground drainage systems where the water may contain sediment, suspended solids, sludge, or floating debris.
Because the sensor is positioned above the flow, there is less need to place the main measurement components directly into the wastewater.
Ultrasonic Flow Measurement
When the pipeline becomes full, the ultrasonic measurement channel provides an additional method for measuring flow velocity.
This is important because the hydraulic condition of a drainage pipeline can change significantly over time.
Instead of using separate instruments for different operating conditions, the integrated system can use the appropriate measurement mode according to the actual pipeline condition.
Water-Level Measurement
The system also measures the water level inside the pipeline.
The water-level information is combined with the known pipeline geometry to determine the wetted cross-sectional area.
The flow calculation system can then combine this area information with the measured flow velocity to determine the flow rate.
How Is an Underground Pipeline Flow Meter Installed?
Installing an underground pipeline flow meter is not simply a matter of fixing the device to the top of the pipe.
The installation location has a direct impact on measurement accuracy.
Even a properly calibrated instrument may produce unstable or less representative results if it is installed in an area affected by strong turbulence, backflow, eddies, obstacles, or sudden changes in pipeline geometry.
For a radar ultrasonic flow meter, both the hydraulic conditions and sensor orientation need to be considered carefully.
1. Choose a Stable and Straight Measurement Section
The preferred measurement location should have relatively calm, stable, and concentrated water flow.
Where possible, choose a straight section of pipeline where the water surface is relatively stable and there are no significant disturbances.
Avoid areas affected by:
- Backflow
- Strong turbulence
- Eddies
- Sudden changes in flow direction
- Obstacles within the measurement area
A stable water surface provides a better measurement environment for the radar sensors.
2. Avoid Bends, Outlets, Confluences, and Sudden Drops
The measurement section should ideally be:
Straight + Stable + Unobstructed
Avoid installing the flow meter close to:
- Drainage outlets
- Flow-control structures
- Baffles
- Pipeline bends
- Pipeline junctions
- Confluence points
- Vertical drops
- Drop manholes
- Sudden changes in pipeline geometry
These locations can create turbulence, backflow, uneven velocity distributions, and unstable water surfaces.
As a result, the measured data may not adequately represent the actual flow condition.
3. Keep Sufficient Distance From Pipeline Junctions
Special attention is required when the proposed installation point is close to a pipeline junction.
If two pipelines converge and one has a higher water level, the flow meter should preferably be installed on the lower-water-level pipeline side, rather than immediately next to the junction.
Where the site layout permits, the measurement point should be positioned at least:
10 × the pipe diameter away from the relevant turning point or junction.
For example, if the pipe diameter is 800 mm, this corresponds to approximately 8 m.
The exact installation position should still be evaluated according to the actual pipeline geometry and hydraulic conditions.
4. Keep the Measurement Section Clear
The selected measurement section should be as unobstructed as possible.
This is particularly important in wastewater and drainage pipelines, where floating debris, garbage, sediment, and other materials may accumulate.
Avoid locations where materials are likely to collect around the measurement area.
A clear measurement section helps reduce:
- Floating debris interference
- Sediment-related disturbance
- Obstruction of the measurement path
- Water-surface instability
The top-mounted design can reduce direct exposure of the main equipment to sediment and suspended solids, but proper site selection remains essential.
5. Install the Sensor in the Correct Orientation
Correct sensor orientation is another important installation requirement.
The flow meter should be installed so that the equipment is parallel to the direction of water flow.
The radar water-level sensor should also be correctly oriented toward the water surface according to the designed installation geometry.
Before tightening the mounting bracket, check that:
- The device is aligned with the flow direction.
- The radar sensor is correctly oriented toward the water surface.
- The radar measurement direction is parallel to the water surface as required.
- The radar beam has a clear measurement path.
- No structural components obstruct the radar beam.
Correct installation geometry helps ensure that the sensors operate under the intended measurement conditions.
Technical Specifications of the Underground Pipeline Flow Meter
After understanding the measurement principle and installation requirements, the following specifications provide a clear overview of the instrument’s technical capabilities.
| Parameter | Specification |
|---|---|
| Power Supply | DC 7–30 V |
| Current Consumption | <160 mA @ 12 V during dual-mode operation |
| Operating Temperature | -40°C to +85°C |
| Radar Velocity Range | 0.03–20 m/s |
| Radar Velocity Accuracy | ±1% FS |
| Radar Velocity Resolution | 0.01 m/s |
| Ultrasonic Velocity Range | 0.02–10 m/s |
| Ultrasonic Velocity Accuracy | ±1% |
| Ultrasonic Velocity Resolution | 0.001 m/s |
| Distance Measurement Range | 0–10 m |
| Distance Accuracy | ±3 mm |
| Distance Resolution | 1 mm |
| Flow Velocity Frequency | 24 GHz |
| Water-Level Frequency | 80 GHz |
| Flow Velocity Antenna | 14 × 32° |
| Water-Level Antenna | 8 × 8° |
| Protection Rating | IP68 |
| Communication Interface | RS-485 |
| Communication Protocol | MODBUS-RTU |
*Actual measurement performance depends on the installation environment and operating conditions.
Wondering Whether This Underground Pipeline Flow Meter is the Right Solution For your Application?
Our engineers will recommend the most suitable model based on your specs and budget.
An underground pipeline flow meter provides a practical solution for flow monitoring in underground drainage systems, wastewater networks, and other large pipelines with complex hydraulic conditions. The system integrates radar flow velocity measurement, ultrasonic flow measurement, and water-level measurement, enabling it to adapt to both partially filled and full-pipe conditions. By combining measured flow velocity, water level, and pipeline geometry, it can calculate the flow rate for continuous monitoring.
By integrating multiple measurement technologies, the system offers greater adaptability to changing hydraulic conditions and enables reliable, continuous flow monitoring. Its non-contact radar measurement and integrated design make it particularly suitable for water supply, drainage, and wastewater applications where conventional flow meters may be difficult to install, operate, or maintain. This provides a practical way to address some of the key challenges associated with monitoring and maintaining underground pipeline networks.
